feat: 实现 Tool Search Tool 动态工具发现机制

- 新增 ToolRegistry 工具注册表，支持核心工具和延迟加载工具分离
- 新增 tool_search 元工具，支持关键词搜索发现可用工具
- 新增基于关键词的搜索算法，按相关度评分排序
- 为所有工具添加 metadata（分类、关键词、延迟加载标识）
- 修改 Agent 支持动态工具注入，tool_search 结果自动添加到可用工具
- 核心工具（tool_search, bash）始终加载，其他工具按需发现

src/tools/filesystem/delete_file.ts

@@ -1,12 +1,20 @@
 import * as fs from 'fs/promises';
 import * as path from 'path';
-import type { Tool, ToolResult } from '../../types/index.js';
+import type { ToolResult } from '../../types/index.js';
+import type { ToolWithMetadata } from '../types.js';
 import { loadDescription } from '../load_description.js';
 import { getPermissionManager } from '../../permission/index.js';
 
-export const deleteFileTool: Tool = {
+export const deleteFileTool: ToolWithMetadata = {
   name: 'delete_file',
   description: loadDescription('delete_file'),
+  metadata: {
+    name: 'delete_file',
+    category: 'filesystem',
+    description: '删除文件或目录',
+    keywords: ['delete', 'remove', 'file', 'rm', '删除', '移除', '文件'],
+    deferLoading: true,
+  },
   parameters: {
     path: {
       type: 'string',